The vehicle wheel bearing apparatus for supporting a wheel rotatably supports a wheel hub to mount via a rolling bearing, a driving wheel and/or a driven wheel. For structural reasons, an inner ring rotation type is used for the driving wheel and both the inner ring rotation type and the outer ring rotation type are used for the driven wheel. In general, the wheel bearing apparatus is classified into a so-called first generation type, second generation type, third generation type and a fourth generation type. In the first generation type, the wheel bearing includes double row angular ball bearings fit between a knuckle and a wheel hub. In the second generation type, a body mounting flange or a wheel mounting flange is directly formed on the outer circumference of an outer member. In the third generation type, one of inner raceway surfaces is directly formed on the outer circumference of the wheel hub. In the fourth generation type, the inner raceway surfaces are directly formed on the outer circumferences, respectively, of the wheel hub and an outer joint member of a constant velocity universal joint.
The wheel bearing apparatus is provided with seals to prevent leakage of grease contained within the bearing apparatus. Also, the seals prevent ingress of rain water or dust from the outside into the bearing apparatus. It is desirable to have an automotive bearing apparatus that has a long life while being maintenance-free. Under the circumstances, it has been proved that many causes of bearing apparatus failure are based on troubles in the seals rather than peeling or breakage of structural elements of the bearings. Accordingly, it is very important to improve the sealability of bearing apparatus in order to extend its life.
Several seals have been proposed to improve their sealability. One example of a wheel bearing apparatus of the prior art where one seal is incorporated is shown in FIG. 7. In descriptions below, the term “outer side” defines a side that is positioned outside of a vehicle body (left-hand side in drawings). The term “inner side” defines a side that is positioned inside of a vehicle body (right-hand side in drawings) when the bearing apparatus is mounted on the vehicle body.
The illustrated vehicle wheel bearing apparatus is a third generation type used for a driven wheel. It includes an outer member 51 formed with a body mounting flange 51b on its outer circumference. The mounting flange 51b is to be mounted on a knuckle (not shown) of a vehicle. The outer member inner circumference includes double row outer raceway surfaces 51a, 51a. An inner member 55 includes a wheel hub 53 and an inner ring 54. The wheel hub 53 is formed at one end with a wheel mounting flange 52. The wheel hub outer circumference includes one inner raceway surface 53a opposing one of the double row outer raceway surfaces 51a, 51a. A cylindrical portion 53b axially extends from the inner raceway surface 53a. The inner ring 54 is press-fit onto the cylindrical portion 53b of the wheel hub 53. The inner ring outer circumference includes the other inner raceway surface 54a opposing the other of the double row outer raceway surfaces 51a, 51a. Double row rolling elements 57, 57 are freely rollably contained between the outer and inner raceway surfaces 53a, 54a of the inner member 55 and the outer raceway surfaces 51a, 51a of the outer member 51.
Hub bolts 52a are arranged on the wheel mounting flange 52 equidistantly along its periphery. The inner ring 5 is axially secured on the wheel hub 53 by a caulked portion 58. The caulked portion 58 is formed by plastically deforming the end of the cylindrical portion 53b. Seals 59, 60 are mounted within annular openings formed between the outer member 51 and the inner member 55. The seals 59, 60 prevent leakage of grease contained in the bearing and the ingress of rainwater and dust into the bearing from the outside.
The outer side seal 59 includes a metal core 61 and a sealing member 62 integrally adhered to the metal core 61, via vulcanized adhesion as shown in an enlarged view of FIG. 8. The metal core 61 includes a cylindrical press-fit portion 61a that fits into the outer member 51. An inner portion 61b extends radially inward from the press-fit portion 61a. The metal core 61 is formed with a substantially “L” shaped cross-section.
The sealing member 62 is formed from elastic material such as synthetic rubber. The sealing member 62 is secured on a radially inner portion 61b of the metal core 61 surrounding the radially inner tip end of the metal core 61. The sealing member 62 includes radially outer and inner side lips 63, 64. The inner side lips 63, 64 bent radially outward so that they are urged onto a ground surface of the base of the wheel mounting flange 52. The sealing member further includes a radial lip 65 arranged on the tip end of the radially inner portion 61b. The radial lip 65 is adapted to be urged onto a ground corner portion 66 of the wheel mounting flange 52.
In addition, a shielding plate 67 is mounted on the outer circumference of the outer member 51. The shielding plate 67 includes a cylindrical portion 67a fit onto the outer member 51 and a standing portion 67b that extends radially outward from the cylindrical portion 67a. The shield plate is formed with a substantially “L” shaped cross section. The standing portion 67b is arranged opposite to the base of the wheel mounting flange 52, via a predetermined gap therebetween, to form a labyrinth seal 68.
The labyrinth seal 68 can prevent the ingress of rain water and dust from the outside. Thus, this ensures a sufficient sealing function although the interference of the side lips 63, 64 of the seal 59 is reduced. Thus, it is possible to reduce friction torque caused by the seal 59 and accordingly to improve the fuel consumption of the vehicle. See, Japanese Laid-open Patent Publication No. 147298/2005.
Thus, it is possible in the prior art wheel bearing apparatus to reduce the friction torque caused by the seal 59. Accordingly, this improves the fuel consumption of the vehicle due to the provision of the labyrinth seal 68. Also, it prevents the ingress of foreign matters 69 such as rain water, muddy water or dust into the inside of the wheel bearing apparatus by two side lips 63, 64 if the foreign matters should pass through the labyrinth seal 68.
However, the ability for flexible deformation of the side lip 63 is substantially detracted when muddy water and dust that enters into a space outside the side lip 63 through the labyrinth seal 68 solidifies. The suppression of flexible deformation of the side lip 63 will not only cause an increase of the rotational torque but will also detract from the desired sealability due to wearing of the side lip 63 caused by sand or dust adhered to the tip of the side lip 63. In addition, the possibility exists that rust will be formed on the outer member 51 and the wheel hub 53 by the muddy water dwelled in the space outside the side lip 63. Thus, not only will the relative rotation between them be obstructed but noise or vibration will be caused by the growing rust. Also, peeled rust will damage the side lip 63 of the seal 59 and thus further detract from its sealability.